This multidisciplinary program in primates emphasizes selected events that influence the reproductive processes before fertilization. The events under investigation include the (1) autoimmune consequences after long-term vasectomy, (2) chemical steps leading to the induction of motility in immature, immotile sperm, and the reversibility of this sequence, (3) role of estradiol-17 beta and progesterone in epithelial and endometrial differentiation in the oviduct and uterus, (4) steroid receptor proteins in the oviduct and uterus, (5) evidence for an oviductal "forward motility protein," (6) role of estrogens and androgens in the regulation of gonadotropins, (7) function of steroid converting enzyme (17-OH dehydrogenase) activities in the uterus, pituitary gland, and hypothalamus, (8) role of androgens in sexual behavior and psychosexual differentiation, (9) factors that regulate the motivation of sexual behavior, and (10) importance of photoperiods in the sexual cycles of prosimians.